In vitro perfusion of juxtamedullary nephrons in rats

studies of rat kidneys revealed the presence of a unique popu-lation of juxtamedullary glomeruli (JMG) located at the inside cortical surface apposed to the pelvic lining and arcuate veins. These “superficial ” JMG were exposed by longitudinally bi-secting the kidney, reflecting the papilla, removing the pelvic mucosa, and transecting the venous walls. A microperfusion system was developed to allow blood perfusion of these neph-rons via arcuate arteries. At a perfusion pressure of 100 mmHg, glomerular capillary pressure averaged 49 t 3 mmHg, with most of the preglomerular pressure drop being localized to the terminal afferent arteriolar segment. In subsequent studies, blood hematocrit was reduced to approximately 30 % with phys-iological solutions devoid of or containing albumin, and rats were treated with a converting enzyme inhibitor. In these conditions, single nephron glomerular filtration rate average